There are many methods of extracting active ingredients from biomaterials. The methods for extracting active ingredients from natural products are solvent exaction (including immersion, leaching, refluxing, boiling), vapour distillation and sublimation, Gao Yuanjun, The development and processing of the wild plants in China, Chinese light industry press, Beijing, 1997.February. The methods to extract natural components are the solvent technology, vapour distillation, and sublimation. The latter two are limitedly used, the solvent technology is used in most conditions, Yao xinsheng, Chemistry of natural drugs, People's Medical Publishing House, Beijing, 1998.June. These methods have many advantages, for example, many kinds of solvent can be used, many active ingredients can be obtained and the extraction yield is higher. However, there are also many shortages, for example, difficulty of separating and purifying, largely denaturing of the active ingredients, much loss of the ingredient by volatilization, and long extraction time, etc. Although several technologies have been developed recently, such as enzyme technology, ultra-micro-pulverizing technology etc., the above shortages are not be eradicated.
The newest technology supercritical CO2 extraction has solved some of the above problems, particularly has a notable advantage of separation and purification, and accordingly has become a very important extraction technology. However, Zhu Zhiqiang described in Supercritical fluid technology, principle and application, Chemical industry press, Beijing, 2000.March: CO2 has lipophilic property. The fragrant oils, fat, alcohol, aldehyde, ketone, wax, the light fraction of resin can be selectively extracted by supercritical CO2 , —saccharides and salts are insoluble in supercritical CO2. The solubility of alkaloids, polysaccharides, steroids, terpenoids, glycosides, saponin or flavonoids, etc. in supercritical CO2 is very poor, which makes it difficult for these substances to be extracted by supercritical CO2 exaction. Additionally, alkaloids, nicotine and caffeine may react with other components, such as citric acid and caffetannic acid, to form salts, which causes it difficult to extract these ingredients by supercritical CO2. In addition, there are other disadvantages of supercritical CO2 extraction, for example, expensive equipment and high cost of operation.